An abrasive tool suitable for grinding sapphire and other ceramic materials is disclosed in U.S. Pat. No. 5,607,489 to Li. The tool is described as containing metal clad diamond bonded in a vitrified matrix comprising 2 to 20 volume % of solid lubricant and at least 10 volume % porosity.
An abrasive tool containing diamond bonded in a metal matrix with 15 to 50 volume % of selected fillers, such as graphite, is disclosed in U.S. Pat. No. 3,925,035 to Keat. The tool is used for grinding cemented carbides.
A cutting-off wheel made with metal bonded diamond abrasive grain is disclosed in U.S. Pat. No. 2,238,351 to Van der Pyl. The bond consists of copper, iron, tin, and, optionally, nickel and the bonded abrasive grain is sintered onto a steel core, optionally with a soldering step to insure adequate adhesion. The best bond is reported to have a Rockwell B hardness of 70.
An abrasive tool containing fine diamond grain (bort) bonded in a relatively low melting temperature metal bond, such as a bronze bond, is disclosed in U.S. Pat. No. Re 21,165. The low melting bond serves to avoid oxidation of the fine diamond grain. An abrasive rim is constructed as a single, annular abrasive segment and then attached to a central disk of aluminum or other material.
None of these abrasive tools has proven entirely satisfactory in the precision grinding of ceramic components. These tools fail to meet rigorous specifications for part shape, size and surface quality when operated at commercially feasible grinding rates. Most commercial abrasive tools recommended for use in such operations are resin or vitrified bonded superabrasive wheels designed to operate at relatively low grinding efficiencies so as to avoid surface and subsurface damage to the ceramic components. Grinding efficiencies are further reduced due to the tendency of ceramic workpieces to clog the wheel face, requiring frequent wheel dressing and truing to maintain precision forms.
As market demand has grown for precision ceramic components in products such as engines, refractory equipment and electronic devices (e.g., wafers, magnetic heads and display windows), the need has grown for improved abrasive tools for precision grinding of ceramics.
In finishing high performance ceramic materials, such as alumina titanium carbide (AlTiC), for electronic components, surface grinding or "backgrinding" operations demand high quality, smooth surface finishes in low force, relatively low speed grinding operations. In backgrinding these materials, grinding efficiency is determined as much by workpiece surface quality and control of applied force as by high material removal rates and abrasive wheel wear resistance.